Method for shelf stable packaging of liquid food in hermetically sealed easy-to-open gable top cartons

ABSTRACT

A method for the shelf stable packaging of perishable liquid food products in hermetically sealed easy-to-open gable top cartons comprising the steps of cold filling liquid food products free from pathogenic and thermophilic organisms into gable top cartons, sealing the cartons over certain critical areas of the seal flaps while reducing or relieving sealing pressure over certain other specified areas, heating the sealed carton up to and holding the contents at a pasteurization hold temperature for a predetermined time and then cooling the contents of the carton.

This application is a continuation-in-part of Ser. No. 07/261,392 filedon Oct. 24, 1988, now abandoned, and entitled Method of Producing ShelfStable Liquid Food Products, and a continuation-in-part of Ser. No.07/261,325 filed on Oct. 24, 1988, now U.S. Pat. No. 4,946,041, andentitled Easy Opening Gable Top Carton.

FIELD OF THE INVENTION

This invention relates to the shelf stable packaging of perishablejuices and other perishable liquid products in hermetically sealed gabletop cartons acceptable to the consumer. A packaged product is said to beshelf stable when it retains its desirable qualities for an extendedperiod of time without refrigeration.

BACKGROUND OF THE INVENTION

The selection of appropriate containers and processes for packaging aparticular liquid food product presents the packer with various optionsfrom which to choose. Against these must be considered numerous factors.These include cost of the container and packaging process, structuralintegrity and weight of the package, handling convenience for the packerand convenience for the consumer i.e., can the container be tightlypacked? Is it fragile? The packer must also consider the distributionnetwork and infrastructure available in the market sought to be served:is refrigeration available, if not, the packaged product must berendered shelf stable?

A package which is too costly in relation to the value of the productitself or which is inconvenient in some respect for the consumer willmeet with market resistance and likely fail to win a sufficient degreeof acceptance to be commercially viable.

Traditionally juices have been packed in cans and glass bottles. Thetechnology applicable to these packages is well known. Juices packed inthese containers may be kept unrefrigerated for extended periodsprovided that these products and their containers have been sterilizedand hermetically sealed in order to prevent entry of bacteria.

These containers have achieved wide acceptance through use. They may beeasily sterilized and sealed effectively. They tolerate both internalvacuum and positive pressure. Closures such as twist off lids forbottles are acceptable to consumers because they are easy to operate andmay be used to close the bottles effectively after first opening. Thesecontainers resist high temperatures and thus may be sterilized at usualtemperatures without deteriorating their structural qualities.

Among the disadvantages of glass bottles and cans are cost and theweight which they add to the product. Also, because of their shape, cansand bottles cannot be tightly packed. In the case of bottles theirrelative fragility is also a disadvantage.

More recently greater use of so-called flexible containers has been madefor the packaging of liquid food products. These include paper-basedcontainers, molded plastic containers and plastic pouches.

Two types of paper-based flexible containers have become widelyaccepted, the gable top carton and the brick pack. The gable top cartonhas been extensively used for packaging refrigerated non-shelf stableliquid products such as milk and other dairy products and fruit juiceproducts. The brick pack, so called because of its shape, has beenextensively used in association with an aseptic packing process forfruit juices packaged for shelf stability and which therefore do notrequire refrigeration.

The gable top carton is relatively inexpensive and light weight.Moreover, because of its planar sides it can be tightly packed forshipping and storage. The gable top carton enjoys wide acceptance in thepublic for its ease of storage and handling after opening and for itsspout which pours well and re-closes effectively even to the extent ofpermitting the contents to be lightly shaken without spilling. Onedisadvantage of the gable top carton, when compared with glass bottles,is the difficulty encountered by many consumers in opening the cartonfor the first time. This problem has been largely overcome in the dairyand fruit juice industry by simply weakening the seal at the spout.

A previously proposed method of weakening the spout is described in U.S.Pat. No. 3,116,002, wherein it is suggested that a non-adherent material"abhesive" be applied to selected areas near the spout in order toreduce the plastic-to-plastic bond formed during the sealing process.This method adds to the cost of the carton and quality control as to theprecise placement of the abhesive is difficult to achieve duringpacking.

While the otherwise desirable goal of achieving a strong hermetic sealis defeated the consumer has become accustomed to the fact that dairyproducts and juices packed in this way must be kept refrigerated andhave only limited shelf lives. Because of this practice of weakening theseal to please the consumer, from a consumer acceptance point of view,it is not possible to successfully market a juice in a gable top cartonunless the spout is relatively easy to open.

Unfortunately, in some ways the gable top carton lacks the structuralintegrity of other containers, especially cans. For instance, gable topcartons are relatively intolerant of internal vacuum or pressure. Alsotheir physical properties make them less tolerant of high sterilizationtemperatures. As discussed below, these drawbacks have inhibited use ofgable top cartons in shelf stable packaging.

Typically, gable top cartons are formed of paperboard sheet materialhaving an overall coating of thermoplastic film such as polyethyleneapplied on the surfaces of the sheet. The plastic coated paperboard isimpervious to moisture and is particularly suitable for use in packagingproducts such as milk and orange juice. The thermoplastic coating notonly serves to moisture proof the carton but also can be utilized forsealing the carton closing flaps which characterize the gable topcarton. This sealing action is accomplished by heating the surfaces tobe sealed while pressing them tightly together to form a liquid tightplastic-to-plastic bond.

The carton erected from the plastic-coated blank typically includes abottom, four sidewalls extending from the bottom and united along theirlateral margins, and an upper closure means which can be opened to forma spout. The closure is formed from four end wall portions united withthe sidewalls and with each other at the lateral margins; the end wallportions are inclined in pairs toward each other and have marginalportions heat sealed to each other which form extensions of the end wallportions; the marginal portions of two opposite end wall portions arefolded like bellows between the outer marginal portions of the tworemaining end wall portions and at least one of the two inwardly foldedmarginal portions is moveable outward together with the pertaining endwall portions from its position between the two outer marginal portionsto a new position outside these where the marginal portion after beingmoved outward, as well as its pertaining end wall portion, form apouring spout and an emptying passage.

Traditionally, dairy products and fruit juices packed in gable topcartons have been kept refrigerated throughout the distribution processin order to avoid almost immediate spoilage. This spoilage would resultfrom the fact that the gable top cartons are not sterilized and thatbacteria in the environment and on the inside of the carton itself woulddevelop very quickly. It is only refrigeration which retards spoilagefor up to a couple of weeks. Products packed in this way are not said tobe shelf stable.

Shelf stability is extremely desirable from many standpoints. A shelfstable product is much less likely to spoil while in the distributionsystem and with a shelf life measured in months rather than days lossesdue to spoilage should be low. The packer does not need to maintain theproduct under refrigeration either in its warehouse or while intransport. Similarly the retailer need not allocate expensiverefrigerated space to store its supply of product. The consumer also hasthe advantage of a product which does not require refrigeration untilopened.

Shelf stability may only be achieved in two ways. First, use may be madeof chemical preservatives. Alternatively, precautions must be taken toexclude the possibility of bacteria coming into contact with the productfollowing pasteurization of the product itself.

In order to achieve shelf stability of a juice or similar liquid foodproduct without using chemical preservatives the product must besterilized (said to be pasteurized). Following pasteurization nobacteria must be permitted to come into contact with the product. Toensure that this is the case, all bacteria which may come into contactwith the product prior to or at the time of filling and sealing of thecarton, all bacteria within the carton and all bacteria in theenvironment which become trapped in the carton after sealing must bekilled. Failure to do so will inevitably lead to spoilage.

With glass containers and cans a process known as post packagingsterilization has been employed to achieve shelf stability. The liquidis poured into a non-sterile container, the container is capped andsealed; the container and its contents are heated to and maintained at asterilization temperature until all the bacteria within the containerare killed; the container is then cooled; the product is then shelfstable.

This process has been used in the brewing and soft drink trade inpackaging liquids in bottles and cans. It has also been used to packageliquids in flexible containers. For example, U.S. Pat. Nos. 4,088,444 toByrne and 2,995,418 to Muller each disclose a sterilization processwherein a container formed from flexible material such as plastic isfilled with a liquid, sealed, and sterilized by first subjecting thecontainer to a hot liquid bath or to steam until the temperature of theliquid in the containers reaches the sterilization temperature,maintaining the temperature at the sterilization temperature untilsterilization is effected, and thereafter cooling the liquid in thecontainers by subjecting the containers to cold water. Muller inparticular specifically contemplates sterilizing fruit juices which arein sealed plastic containers.

U.S. Pat. No. 4,376,126 to Evers discloses a method of making a yogurtbeverage which includes the steps of pasteurization or sterilizationafter the beverage has been packed in a container. Evers, however, doesnot appear to specifically disclose the use of any particular containernor does he mention the special problems associated with gable topcartons.

U.S. Pat. Nos. 4,057,391 to Yamaguchi, 3,481,688 to Craig et al. and2,380,134 to Waters disclose methods of preserving or sterilizing foodin flexible containers, such as plastic containers, whereby the food issubjected to heating and then cooling after being sealed in thecontainers. However, these patents do not specifically teach thesterilization of liquid food products, such as fruit juices nor do theyaddress the special problems associated with gable top cartons.

U.S. Pat. No. 237,449 to Schaumberg et al. discloses a method ofpreserving fruit juices in glass bottles that includes bottling andsealing the juices and thereafter heating the juices to 170° F. for 35minutes. However, Schaumberg et al. does not disclose subjecting theheated bottles to a cooling process and does not contemplate the use ofplastic or plastic coated cartons nor does he address the specialproblems of gable cartons.

Despite the wide recognition of the usefulness of most packagesterilization in order packaging systems, the process has not to theinventor's knowledge previously been used to package perishable liquidsin gable top cartons.

Since the introduction in the 1950's of paper-based cartons for liquidfood products, only two processes have been widely promoted in order topermit paper-based cartons to be used for packaging shelf stableproducts. These are the aseptic process, promoted since the early 1960'sby Tetra Pak of Sweden principally in association with the so-calledbrick pack, and the hot fill process more recently adapted for gable topcartons from a process used in connection with glass bottles.

In accordance with the aseptic process the product is pasteurized andkept in a sterile environment up to and through the filling and sealingof the container which is pre-sterilized (generally using hydrogenperoxide and steam) and also kept in a sterile environment until fillingand sealing. The seal must be hermetic under all conditions. Asepticallyprocessed brick packs must be cut, pierced or torn to open. In each caseeither the opening or the re-closing is clumsy and is not consideredadvantageous from a consumer convenience point of view. The asepticmethod is complicated to carry out and requires specialized andexpensive equipment.

Notwithstanding the complexity and cost of the aseptic process it becamewidely accepted in Europe, Australia and Canada in the 1970's. It wasonly approved in the United States in the early 1980's and has becomewidely accepted since that time. Prior to the introduction of theaseptic process and the brick pack there were no shelf stable productspackaged in paper-based containers. The aseptically packed brick packcreated a whole new application for paper-based containers. The successof the aseptically packed brick pack has been nothing short ofphenomenal. It is estimated that, on a worldwide basis, asepticallypacked brick packs account for over $20 billion dollars worth of liquidfood products.

Because of the complexity and cost of the aseptic process, efforts weremade to achieve shelf stability in paper-based containers, mostdesirably with the popular gable top carbon, with simpler less expensivetechnology. In the early 1980's a so called hot fill process wasproposed.

A less costly alternative to the aseptic method, the hot fill method didnot meet with much success. In accordance with the hot fill method thepasteurized product is heated to temperatures in the range of 185degrees F. and poured hot directly into the gable top carton which isthen sealed. The heat of the product itself kills the bacteria remainingwithin the container after sealing.

In the United States the hot fill method for gable cartons was adoptedby various juice packers but has largely been abandoned because thismethod results in a substantial vacuum being created within thecontainer following the cooling of the product from the hot filltemperature to room temperature. This vacuum is undesirable because itpromotes the inflow of bacteria from the environment through the sealwhich leads to quick spoilage unless the product is refrigerated. Inorder to deal with this problem the seal must be strong enough towithstand the significant pressure differential created by the process.The seal must also be strong enough to retain its integrity in all casesthroughout the distribution process. If at any time seal integrity islost, the vacuum will cause bacteria to enter the carton and virtuallyimmediate spoilage to occur.

Where the seal was made sufficiently strong to prevent the entry ofbacteria under all conditions, the cartons were so hard to open thatconsumers, used to the ease of opening of the weakly sealed gablecartons used for dairy products, resisted the container.

In practice, the strength of the seal which has to be provided toovercome the problems created by the high vacuum resulted in asignificant percentage of the cartons not being readily openable by theconsumer in the ordinary way. This was such a problem that InternationalPaper, the principal proponent of the hot fill technology, developed analternative form of opening the carton, subject of U.S. Pat. No.4,527,732 issued in 1985, which covers a scored "smile" to be pushedthrough by the consumer.

Thus up until the present invention industry efforts to adapt thepopular gable top carton to achieve shelf stability and yet retain itsgood opening and handling qualities all at reasonable cost haveheretofore not proven successful; and this despite the fact that findingan uncomplicated and inexpensive method of achieving shelf stabilitywith a gable top carton would open up a market worth at least severalhundred million dollars for cartons alone.

Thus, there remains a need for a system for shelf stable packaging ofperishable liquids which allows use of a gable top carton which can behermetically sealed to ensure shelf stability while retaining an easilyopened spout necessary for consumer acceptance.

SUMMARY OF THE INVENTION

The present invention overcomes the difficulties referred to above inadapting the gable top carton for the packaging of shelf stable liquidproducts such as juices in a manner acceptable to the consumer. Thepresent invention is, to some extent, the consequence of the presentinventor's recognition of a significant interrelationship between thestrength of seal necessary to maintain hermeticity and the process usedto sterilize the gable top carton.

Having recognized this, the present inventor has determined that thelack of commercially viable system for shelf stable packaging in gabletop cartons is primarily due to a failure to find an acceptablecompromise between hermetically sealing and ease of opening of thesealed spout of the gable top carton. These two objectives arediametrically opposed; the stronger the seal, the harder it is to openand the lesser the consumer acceptance.

The present inventor has discovered that shelf stability with an easy toopen gable top carton can be achieved through the selection of anappropriate post-pasturization process combined with an appropriate sealdesign. The inventor has also discovered that an adequate seal which isstill easy to open can be achieved by applying increased pressure atcertain empirically located critical points along the seal. If thesecritical points are adequately sealed, the remainder of the seal can besealed in an easy open fashion. Consequently, the spout is still easy toopen.

In summary, the inventor has discovered a technique for achieving theshelf stable packaging of perishable liquids in a gable top carton whichis easy to open. The technique involves the combination of a techniquefor sealing a liquid in a gable top carton and a process for sterilizingthe interior and contents of the sealed carton.

In accordance with the present invention, the liquid food product to bepacked is first pasteurized, if required, in accordance with proceduresappropriate to the particular product. The product is then cooled toroom temperature and introduced into gable top cartons which are thensatisfactoily hermetically sealed at the empirically determined criticalpoints along the sealing portion of the gable top carton in accordancewith the method described below in such a way as to permit their ease ofopening for the consumer. The filling process is open to theenvironment.

The sealed cartons are then heated to and held for an appropriate timeat a post-pasteurization temperature appropriate to kill theenvironmental bacteria, mold and yeast remaining within the product andwithin the carton but at a temperature below that which would melt theinner plastic layer of the carton or cause delamination of the carton.Generally a post-pasteurization temperature in the range of about 160°F. is appropriate with a preferred temperature of about 167° F. with aholding time of about 10 minutes. The cartons are then cooled. Becausethe contents were originally sealed in the carton at room temperatureand returns to room temperature after being heated, no vacuum is created(i.e. no pressure differential across the seal) and thus there is nodanger that environmental bacteria will be drawn into the carton in theevent the integrity of the seal is subsequently lost. While the seal ishermetic, it need not be as strong as that required if the hot fillprocess were used and is therefore more acceptable to the consumerbecause the carton remains easy to open.

The present invention offers significant advantages over the hot fillmethod. With the present invention the desirable easy openingcharacteristics of the gable top carton may be retained which is notpossible with the hot fill method because the seal must be very strongin order to overcome the pressure differential across the seal createdby that process. In the event that seal integrity is lost or a leakoccurs in a container packed by the hot fill method, the internal vacuumwill immediately draw harmful microorganisms into the container whichwill lead to spoilage. With the present invention, because there is novacuum in the head space above the liquid in the carton, a minor breakin the seal or leak elsewhere will not result in microorganisms beingdrawn into the carton and thus spoilage will be avoided.

As compared with the aseptic process, the present invention requiresmuch less sophisticated equipment which is both less costly and easierto operate. It is estimated that, taking into account capital costs andoperating costs, the present invention can be worked for approximately50% of the cost of the aseptic process in operations of a certain size.The present invention is also more secure than the aseptic process.Packing in the aseptic process must be done in an entirely asepticenvironment. If, because of equipment or operator problems, any bacteriashould find their way into the product or the container after they havebeen separately sterilized and before the package is sealed, thenspoilage will occur. The present invention permits the filling to bedone in an open environment because the bacteria are killed after thepackage is sealed and no further opportunity for bacteria to enter thecarton occurs.

Another advantage of the present invention over the aseptic process isthat the present invention does not require a sterilizing agent such ashydrogen peroxide. With the aseptic process it is always possible thattraces of hydrogen peroxide remain on the inside surface of thecontainer and contaminate the product. The use of hydrogen peroxide alsopresents a problem for workers packing the product. If for any reasonthe ventilation system required to evacuate hydrogen peroxide vapoursshould not operate properly, the atmosphere in the packing area may veryquickly become contaminated and pose a health hazard to the workers. Thepresent invention presents no such danger.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a conventional gable top carton havingan arrangement in a closed state;

FIG. 2 is a perspective view of the package of FIG. 1 in an open state;

FIG. 3 shows part of a blank for making a gable top carton;

FIG. 4 is a perspective view of a gable top carton according to thepresent invention;

FIG. 5 shows the carton of FIG. 4 partially opened;

FIG. 6 shows the carton of FIGS. 4 and 5 opened up to show the heatsealed areas.

FIG. 7 is a view of a die used to seal the carton of FIGS. 4 and 5.

FIG. 8 is a perspective view of a gable top carton in accordance withanother embodiment of this invention illustrating the opening of thecarton;

FIG. 9 is a perspective side elevation view of the female portion of adie for producing the embodiment of FIG. 8; and

FIG. 10 is a perspective side elevation view of the male portion of adie for producing the embodiment of FIG. 8.

FIG. 11 is a perspective view of an improved male jaw for sealing agable top carton;

FIG. 12 is a perspective view of an improved female jaw for sealing agable top carton;

FIG. 13 is a cut-away view of a gable top carton;

FIG. 14 is a side view of the top of a gable top carton.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1-3 show a conventional gable top carton construction.

The package shown in the drawings has four sidewalls 1 and a bottom (notshown). Furthermore, the package has four end wall portions 2 which areunited on one hand with the sidewalls 1 and on the other with eachother. At the upper free margin, the end wall portions 2 are providedwith marginal portions 3 and, 4 which are folded toward each other insuch a way that opposite end wall portions 2 are inclined in pairstoward each other and that the marginal portions 3 of two opposite endwall portions lie folded like bellows between the marginal portions 4 ofthe two remaining end wall portions. Thus, the end wall portions 2 whichare provided with the inwardly folded marginal portions 3, will, asshown in FIG. 3, be divided into three essentially triangular portions,the intermediate one 5 of which extends between the end wall portions 2provided with the outer marginal portions 4, while the two side portions6 rest against the inside of each of each one of these.

The gable top carton is constructed from sheets of material whichinclude at least a basic outer layer of cardboard and an inner layer ofthermoplastic material. Normally, the sheet is entirely plastic coatedand can include additional barrier layers. The preferred structuralmaterial of the present invention is in five layers, namely, an innercoating of polyethylene and aluminum (or other satisfactory barriermaterial) barrier, another polymeric layer to bond the foil, a layer ofpaper board and an outer layer of polyethylene or lacquer. A sixthlayer, usual for hot filling methods, is not needed with the presentinvention. Suitable plastics for the carton also include vinyl resins,such as polyvinyl chloride, regenerated cellulose, polypropylene,polyethylene terephalate, polycarbonates and other plastics that areused for food products. Where a barrier layer is to be used, ethyl vinylalcohol or like barrier film may be substituted for foil. The sealing ofthe package with the marginal and end wall portions in the positionshown and described is brought about by means of heat, which will fusethe thermoplastic layers with the sealing zone.

When the package is to be opened, the seal is torn open over one half ofthe sealing zone, whereupon the inwardly folded marginal portion locatedin said zone is pulled out to the position shown in FIG. 2, where themarginal and the end wall portions will form a pouring spout.

FIG. 3 shows part of a blank for a package of the indicated kind. Thedrawing shows essentially only that part of the blank which is to formthe inside surface of the marginal and end wall portion of the package,which can be opened. The blank is provided with fold or score linesalong which the blank is to be folded as to form the finished package.

Referring now to FIGS. 4 and 6, the carton illustrated is mainly ofconventional construction. It includes opposed pairs of side walls 10and 11, connected by a fifth panel 12. There is a bottom closure 13 anda gable top generally indicated at 14. The gable top includes a pair ofside panels 15 having fold or score lines 16 to facilitate opening and apair of end panels 17 having fold or score lines 18. A pair of top orside flaps 19 are extensions of side panels 15 and extend somewhathigher than end flaps 20 that are an extension of end panels 17. Sideflaps 19 are heat sealed in face to face relationship as shown. Flaps 19and 20 splay at horizontal fold line 27 to form the top of the carton.End flaps 20 are heat sealed to the interior of the lower parts of sideflaps 19 as shown in FIG. 5.

Both in the case of hot fill and for non-shelf stable packed juices anddiary products flaps 19 and 20 are sealed over their entire surfaces. Itis also known to provide further additional optional sealing such as apair of vertical stake lines 21 at the end that is not to be opened andwhich coincides with the fifth panel 12. Optionally, at the other endthere is stake line 21a. There may also be a horizontal stake line 22extending across the side flaps 19. Stake lines are strongly indented togive a more secure seal. There may also be a center stake point 70 whichpresses together, expands into abutment and seals the adjacent edges ofthe inwardly folded end flaps 20. The foregoing is conventionalstructure.

The present inventor has discovered that, in combination with anappropriate post-pasturization process, the said optional sealing areasare the truly critical ones. If these are made then it is not necessaryto seal flaps 19 and 20 uniformly over their entire surfaces. Havingrealized this the present inventor empirically discovered what specificareas other than the critical areas should be sealed and the extent ofsuch seal in order to achieve the desired easy opening characteristic ina shelf stable gable top carton.

Since sealing at the critical areas is sufficient to ensure that, incombination with the post-pasturization process selected, the seal willin a commercially acceptable percentage of cases keep bacteria out ofthe carton, the non-critical areas, i.e., the areas which are notstaked, can be selectively sealed lightly or not at all to make thecarton easy to open. One such construction is shown in FIGS. 4-6.

The difference from conventional structure according to this embodimentis in the area of the seal between side flap 19 and end flap 20.According to conventional practice in the case of hot fill, the whole ofthe interior of end flaps 20 are sealed to side flaps 19. According tothis invention an area which may be in the shape of an inverted triangleor a notch or a sector is left unsealed or lightly sealed at the topcenter of end flap 20 as indicated by the numeral 25 in the broken awaypart of FIG. 5. The remaining sealed area is stippled and indicated at24. In FIG. 6 the unsealed or lightly sealed area is shown at 23a and23b which combine to provide area 23 when the carton is closed. It hasbeen found that, particularly when the stake point 70 is located at theapex of triangle 25, an effective seal is provided in spite of thisunsealed or lightly sealed area. The unsealed area at the top centerenables the consumer to start opening the carton and also results inthere being less seal to pull apart where the consumer has the leastleverage.

FIG. 7 illustrates the male jaw of a suitable die 30 including die faceportion 31 for pressing together the upper part of side flaps 19, dieface portions 32 and 33 for the ends and horizontal stake embossing line34, vertical stake embossing lines 35 and embossing protrusion 36 forthe center stake point. Die face portion 37 which presses flaps 19 and20 together is cut away at 38 to leave a triangular unsealed or lightlysealed area. This can be used with a matching female die.

Alternatives for providing the desired unsealed area would include theuse of silicone as a parting agent or "abhesive" to prevent adhesion inarea 25. Another possibility if adhesives were used in place ofspecifically made heat sealing jaws would be to omit adhesive in area25. These methods are generally more expensive and less reliable becauseof the risk of misalignment of the parting agent to the desirednon-adhering area. Thus, heat sealing with specially patterned jaws isthe preferred method of closure where, as usual, the carton is coatedinternally with a thermoplastic resin.

FIG. 8 illustrates an improved structure which is similar to thatillustrated in FIGS. 4 to 6 but showing an unsealed or lightly sealedarea at the top of flap 20 immediately above stake point 70substantially in the shape of a rectangle 25a instead of the triangle ofFIG. 5 and showing a further unsealed or lightly sealed area 25bextending between stake point 70 and vertical stake line 21a. Areas 25aand 25b are left unsealed or are lightly sealed by providing a die whichapplies no pressure or little pressure in these areas.

The construction of a suitable die is illustrated in FIG. 9 showingfemale jaw 41 and FIG. 10 showing male jaw 40. Referring now to FIG. 10,male jaw 40 has a die face 42 having a raised longitudinal rib 43 toprovide a horizontal stake line and vertical ribs 44 and 45 to providevertical stake lines on the side of the container that is to remainsealed and a vertical rib 46 to provide a vertical stake line on thespout end of the carton (i.e. the end that is to be opened). Male jaw 40has a set screw 47 to provide a central stake point 70. The generallyrectangular relieved area 25a of FIG. 8 is provided by depressed area 48immediately above set screw 47 and offset in the direction of the sideof the carton that is to be opened. A relieved area 49 is also providedextending from set screw 47, which provides center stake point 70, torib 46 which provides vertical stake line 21a. Male jaw 40 also includesarea 50 for sealing side flaps 19 of the carton and areas 51, 52, 53 and54 for sealing the remainder of end flaps 20.

Female die 41 shown in FIG. 9 has an upper area 55 which mates withportion 50 of the male jaw and a slightly undercut area 51 the upperedge of which is located to accomodate rib 43. Die 41 has slots 56 and57 to accomodate ribs 44 and 45 and slot 58 to accomodate rib 46. Italso has a depressed area 59, to relieve pressure, matching area 49 ofthe male die and generally rectangular pressure relieving area 60matching area 48 of the male die.

FIGS. 11 and 12 show an even further improvement of the male and femalejaws respectively. The jaw construction shown therein is similar to thatshown in FIGS. 9 and 10 where similar reference numerals are used.However, there are several differences which have been empirically foundto yield better results. The differences reside in the region below thelongitudinal rib 43 and between rib 45 and rib 46. It should be notedthat in all of FIGS. 9-12, the depth of the depressions relative to oneanother is exaggerated for emphasis. In FIG. 11, the set screw 47 usedto define the stake point in the jaws shown in FIG. 10 is replaced witha protrusion 471 which may be of semi-circular shape as shown. Theprotrusion 471 is in fact recessed from the longitudinal rib 43 butextends out generally as far as the ribs 44, 45 and 46. The male jawalso includes a recessed portion 53 like that of male jaw shown in FIG.10, but the recessed portion 53 includes an inclined recess portion 494recessed at an angle of about 30° to 40° with one edge contacting therecessed surface 53 and one edge extending significantly below thatsurface. Another surface 492 is recessed from the recess surface 53 and,optionally, a further recessed portion 491 is recessed from the portion492.

The female jaws shown in FIG. 12 are similar to the female jaws shown inFIG. 8 with the exception of modification made in the depressed area 59.Specifically, in the modified jaw, the depressed area 59 issignificantly depressed. From this depressed area are provided a numberof areas which are less depressed, i.e., protrude from the depressedarea 59. These include the areas 60 and 58 and a protruding area 472which is adapted as a stake plate for protrusion 471 in the male jaw toprovide a heavily staked area.

A protrusion such as 36, 47 or 471 is necessary to create a center stakewhich will block the natural path bacteria might follow to enter thecarton. This path would be from the edge of the carbon along a channel28 just above the upper edges 20a of end flaps 20 as shown in FIGS. 13and 14 and down into the carton between the folding points of end flaps20 where a natural gap 29 occurs. Accepted practice dictates that thelarger the center stake in the gap region 29 the better.

The present inventor has discovered that to ensure the easy opencharacteristic desired the center stake should be optimally placed belowand as close to the upper edge of the end flaps as possible with a shapeand area sufficient to adequately close the gap 29 and no more such asshown at 71 in FIG. 14. The present inventor has further discovered thatif this is done and area 26, being the intersection of the fold or scorelines on panel 17, is left substantially unaffected by the center stake,this area will "pop" out during the opening process and greatlyfacilitate the opening of the carton. It is believed that thisarrangement allows sub-panels 17a and 17b to toggle effectively withoutdistortion and thus bring greater force to bear in breaking the seal.

Although the location and dimensions of the stake areas and thecorresponding design of the jaws have been derived empirically, it hasbeen found that generally the critical areas are those areas necessaryto ensure a minimum complete seal of the flaps. Further, it has beenfound that, by relieving sealing pressure immediately adjacent tocritical areas, improved sealing is achieved. Specifically, when theareas immediately adjacent the critical areas are relieved the forceapplied by the jaws to seal the flaps occurs at a reduced area, i.e.only at the critical areas. Accordingly, when a constant amount ofpressure is applied to the jaw, the provision of a recessed areadecreases the area of contact upon which high pressure is applied andthus increases the sealing pressure per unit of area over the criticalareas; as a result, a stronger seal without an increase in pressureapplied to the jaws.

Traditionally, gable top cartons were heat sealed evenly across theflaps by flat non-patterned planar jaws. The practice then developed tofurther strengthen the seal by adding horizontal and vertical stakes anda center stake. It is believed that until the present invention, it wasnot understood that, so long as a process could be developed which wouldnot create any significant pressure differential across the seal, apractical seal could be achieved by relying principally on the sealingeffect of the horizontal, vertical and center stakes. With thisrealization it became possible to relieve sealing pressure, and thus thebond strength between the flaps forming the seal, over those other areaswhich would significantly improve the opening characteristics of thecarton.

The sealing of the gable top carton can be accomplished by employing thetechniques described above so as to ensure a strong seal at certaincritical areas while maintaining an easy to open carton. To ensure thatthis seal is adequate to ensure shelf stability, however, the contentsmust be sterilized or pasteurized in such a way that a stronger seal isnot required and additional forces are not applied to the seal. As notedabove, this means that the so-called hot fill method of pasteurizationis not acceptable because it results in a vacuum which requires astronger seal.

The present inventor has discovered that by combining the sealingtechnique described above with the following post-packagingpasturization process, traditional gable top cartons can be used topackage shelf stable liquid products and simultaneously retain theireasy opening characteristic required in order to achieve consumeracceptance.

It is believed that no such practical process has previously beendeveloped for post-packaging pasteurization in easy to open gable topcartons constructed of plastic or paperboard coated with plastic.

In accordance with one aspect of this invention, the method of providingliquid food products that are shelf stable in easy to open gable topcartons comprises the steps of:

(a) cold filling a plastic coated gable top carton with an essentiallynon-carbonated liquid food product free from pathogenic and thermophilicorganisms;

(b) sealing the carton as described above;

(c) heating the food product in the carton to a pasteurization holdtemperature in the range of about 160° F. and preferably 167° F. butbelow the softening temperature of the plastic;

(d) maintaining the food product at the pasteurization hold temperaturefor sufficient time to provide an adequate kill of the bacteriaremaining within the carton; and

(e) cooling.

The food products to which this invention is applicable are those whichare generally pourable and could be advantageously packaged in gable topcartons, including, for example, liquid dairy products, non-carbonatedfruit products such as the citrus products or citrus flavored products,fruit products, vegetables juices and vegetable cocktails. Carbonationmust be avoided as otherwise the pressures that would be generated inthe carton during the process would be too high.

Another requirement of the food product is freedom from pathogenic andthermophilic bacteria. Most juices and drinks have pH's in the range2.8-4.0 and not above pH 4.6. At a pH above 4.6 there is a potentialproblem of pathogenic bacteria. Below pH 4.6 the problems are yeast,molds and bacteria.

If the pH is above 4.6, which would include such products as milk, thenthere should be a preliminary ultra high temperature treatment at 240°F. to 260° F. for 15-20 seconds to kill pathogenic organisms, followedby cooling to ambient temperature. A preliminary ultra high temperaturetreatment is advisable with some vegetable base products such as tomato,due to their initial high content of thermophilic molds.

The juices and drinks to which this process is applicable are formulatedin a tank at ambient temperatures in the range 40°-75° F. and pretreatedas discussed above if necessary. They are then pumped to a fillingstation where the juice or drink is fed into cartons.

Although not essential, it may be useful to provide a sparging infusionvalve in the line between the tank and filling station. The sparginginfusion valve is used to add up to about 0.1 lbs/square inch ofnitrogen or carbon dioxide, and preferably about 0.01 lbs/square inch.The purpose of sparging is to create a slight positive pressure tooppose the entrance of any bacteria into the carton after filling.Carbon dioxide is preferred for this purpose. The product sparged withcarbon dioxide would have such a small amount of carbon dioxide that itwould not be classified as a carbonated product.

At the filling station which is of conventional type, a number ofindividual cartons are filled cold. The temperature of the liquid foodproduct should be less than 80° F. and desirably less than 70° F. toachieve a neutral or positive pressure after filling. This may becontrasted with hot fill temperatures of the order of 180° F. Themaximum temperature that can be used depends on the conditions includingthe positive pressure from any sparging gas and on the strength of theseal. After filling and closing the cartons there should be a neutral toslightly positive pressure. As previously indicated a vacuum isundesirable.

The cold filled cartons are transferred to a processor comprising threezones, a preheat zone, a hold zone, and a cool zone.

The processor may be in the form of a continuously moving chain uponwhich rows of cartons are placed. The cartons are spaced to allow waterto run down the sides of the cartons to heat or cool the contents.Heating may also be achieved in other ways such as the use of microwaveenergy provided no metal is used in the carton structure.

1. Preheat zone

The cold filled cartons are preheated preferably by pouring water at atemperature of 180° F.-185° F. onto the cartons and allowing it tocascade down the sides. After a period of time that varies with the sizeof the carton, viscosity, solids content, etc., the liquid productwithin it reaches the desired "pasteurization hold" temperature. Thepreferred temperature for "pasteurization hold" is about 167° F., whichwill be reached in about 13-19 minutes in the case of 1 liter cartons.Two liter cartons would take 20 to 24 minutes to reach this temperature,while 4 to 7 minutes would be adequate for 250 ml. cartons. If microwaveenergy were used to heat the product, the time to reach thepasteurization temperature may be different.

2. Hold zone

The product is maintained at the required pasteurization temperature fora predetermined time to ensure adequate kill of all microorganisms. Theappropriate time at various "pasteurization hold" temperatures isavailable from standard texts. At the preferred temperature of 167° F. ahold time of ten minutes is recommended. The temperature should not begreater than about 174° F., at which the time will be about 4 minutes,as otherwise there may be problems with softening of the plastic wherethe carton is polyethylene and delamination of foil from paperboard willoccur. Slightly higher temperature may be used with plastics having ahigher softening point such as polypropylene. At lower temperatures thehold time is quite long. For example, at 160° F. it would be about 25minutes.

3. Cool zone

After holding for the required amount of time, the cartons go into acooling zone which, if water chilled, may exit at around 90° F. to 105°F. This temperature is desirable as it will quickly evaporate off anyexcess moisture adhering to the carton.

The temperature of the cooling water may be about 35° F. to 60° F. Thecartons then leave the processor and are packed in cases.

The process is further illustrated by the following examples:

EXAMPLE 1

This example relates to the production of 1000 Imperial gal. of singlestrength (ready to drink) orange juice. 135 gal. of orange juiceconcentrate 65 Brix (% soluble solids) is added to 865 gal. of water andblended for 10 minutes. It is then pumped using positive pumps through aline leading to a filler. The line includes a sparging infusion valve tosparge carbon dioxide to give an end product with about 0.1 lbs/squareinch of gas. At the filler the carton is filled at a temperature ofabout 70° F. into one liter gable top cartons which are heat sealed inaccordance with the sealing technique described above. The cartons arebrought up to a temperature of 167° F. in 14 minutes and held at thattemperature for 10 minutes. They are then chilled with water at 40° F.for 12 minutes to give an exit temperature of 90° F. The orange juicehas a desirable shelf life of three months and a recommended maximum ofsix months. The taste of the orange juice is markedly better than thatproduced by hot filling.

EXAMPLE 2

This example relates to a Caesar's clam juice cocktail. A thousand imp.gal. batch was made of water and 100 imp. gal of tomato paste (32-34brix) 650 lbs of salt; 60 lbs of monosodium glutamate; 700 lbs ofglucose solids; 30 lbs of spices and 10 gal. of clam broth. It is pumpedto a pasteurizer where the product is brought to a temperature of 250°F. in about 10-20 seconds, and held at this temperature to 48 to 52seconds, cooled at 70° F. and then filled and processed as described inExample 1.

EXAMPLE 3

This example relates to the packaging of milk in a shelf stable easy toopen gable top carton. The milk is first pasteurized at a conventionalUHT temperature such as 250° F. for approximately 8 seconds thenimmediately cooled to ambient temperature. The milk is then cold filledinto gable top cartons in the normal manner under stringent sanitaryconditions and then sealed and processed as described in Example 1.

I claim:
 1. A method of shelf stable packaging a perishable liquid foodproduct in a gable top carton which is internally coated withthermoplastic and which includes sealing flaps which comprise side flapsand inwardly folded end flaps, the lower edge of each of said flapsbeing defined by a horizontal fold line where the flaps splay to formthe top of the carton, each of the flaps having an upper edge, the upperedge of the side flaps extending beyond the upper edges of the endflaps, one set of which end flaps being outwardly foldable to form aspout, the method comprising the sequential steps of:a) ensuring thatsaid liquid food product is free from pathogenic and thermophilicorganisms; b) filling the carton with the liquid food product maintainedat substantially room temperature; c) hermetically sealing the cartoncontaining said liquid food product at substantially room temperature byapplying heat and a first predetermined amount of pressure topredetermined portions of the sealing flaps, said predetermined portionsincluding:i.) a horizontal stake line extending the full length of theside flaps at a level just above the upper edge of the end flaps; ii.)at least one vertical stake line located inwardly of at least one end ofthe flaps extending downward from the horizontal stake line to thehorizontal fold line; iii.) a center stake located at the centralportion of the side flaps in the vicinity of the junction of theinwardly folded end flaps, said center stake being of a size and shapesufficient to cover portions of both the end flaps and being locatedabove the horizontal fold line, said stake lines and center stake beingconfigured and positioned and said first predetermined amount ofpressure and heat applied to said stake lines and said center stakebeing sufficient to create hermetic seals at these portions of saidsealing flaps, and applying lesser amounts of pressure to other portionsof the sealing flaps, said lesser amounts of pressure being sufficientto provide a seal at these other portions that in combination with theseal provided at the stake lines and at the center stake results in anoverall hermetic seal which prevents bacteria and air from entering thecarton through the sealing flaps, but which said lesser amounts ofpressure, if applied across both said predetermined portions and saidother portions of the sealing flaps would not provide a seal sufficientto prevent bacteria and air from entering the carton through the sealingflaps; wherein the overall effect is to provide a carton that is easierto open than a carton in which all of the sealed portions of the sealingflaps have been sealed with the first predetermined amount of pressure;d) heating the food product in the sealed carton to a temperaturesufficient for pasteurization but below the softening temperature of thethermoplastic coating; e) maintaining the food product at thepasteurization temperature for sufficient time to kill essentially allmicroorganisms remaining within the sealed carton; and, f) cooling thegable top carton and its pasteurized contents.
 2. A method as in claim 1in which the said other portions over which less pressure is appliedinclude a first area between the upper edge of the end flaps and thehorizontal fold line which area extends from the center stake regionoutwardly toward the spout end of the carton.
 3. A method as in claim 2in which the first area is in the shape of a triangle tapering towardsthe spout end of the carton.
 4. A method as in claim 2 in which thecenter stake is located above a point mid-way between the upper edge ofthe end flaps and the horizontal fold line.
 5. A method as in claim 2 inwhich pressure is further relieved over a second area extending belowthe upper edge of the end flaps between the center stake and thevertical stake on the spout end of the carton.
 6. A method as in claim 1in which the said other portions over which less pressure is appliedinclude an area extending below the upper edge of the end flaps betweenthe center stake and the vertical stake on the spout end of the carton.7. A method as in claim 6 in which the pressure over the area to whichless pressure is applied is relieved progressively from the horizontalstake line down.
 8. A method as in claim 1 in which the center stake islocated above a point mid-way between the upper edge of the end flapsand the horizontal fold line.
 9. A method as in claim 1 in which thepredetermined portions of the sealing flaps include:a) a center stake ofa size and shape sufficient to cover portions of both of the end flapsand being located above a point mid-way between the upper edge of theend flaps and the horizontal fold line; and where, b) pressure isfurther relieved over a first area between the upper edge of the endflaps and the horizontal fold line which area extends from the centerstake region outwardly approximately one third the distance toward thespout end of the carton; and, c) pressure is progressively furtherrelieved from the horizontal stake line down over a second areaextending below the upper edge of the end flaps and centeredapproximately two thirds of the way between the center stake and thevertical stake on the spout side of the carton.
 10. A method as in claim1 in which the pasteurization hold temperature is in the range of 160 F.to 174 F.
 11. A method as in claim 1 in which the thermoplastic ispolyethylene and the pasteurization hold temperature is in the range of160 F. to 174 F.
 12. A method as in claim 1 in which the pasteurizationhold temperature is about 167 F.
 13. A method as in claim 1 in which thefood product is maintained at a pasteurization hold temperature of about167 F. for about 10 minutes.
 14. A method as in claim 1 in which afterpasteurization the food product is cooled by chilled water to atemperature of about 90 F. to 105 F.
 15. A process for packaging aperishable liquid product free from pathogenic and thermophilicorganisms in a shelf stable gable top carton which includes sealingflaps which comprise side flaps and inwardly folded end flaps, one setof which end flaps is outwardly foldable to form a spout, the processcomprising the sequential steps of:a) cold filling the gable top cartonwith the product; b) hermetically sealing the carton containing saidliquid food product at substantially room temperature by applying afirst predetermined amount of pressure to predetermined portions of thesealing flaps that is sufficient to create hermetic seals at thesepredetermined portions of said sealing flaps, and applying lesseramounts of pressure to other portions of the sealing flaps,said lesseramounts of pressure being sufficient to provide a seal at these otherportions of the sealing flaps that in combination with the seal providedby the first predetermined amount of pressure results in an overallhermetic seal which prevents bacteria from entering the carton throughsaid sealing flaps, but which lesser amounts of pressure would not alonebe sufficient to prevent bacteria from entering the carton through thesealing flaps if applied across the entire sealing flaps, wherein thecarton is easier to open than a carton in which all of the sealedportions of the sealing flaps have been sealed with the firstpredetermined amount of pressure; c) heating the product in the sealedcarton to a pasteurization hold temperature which is above thepasteurization temperature of the product; d) maintaining the foodproduct at the pasteurization hold temperature for sufficient time toprovide an adequate kill of microorganisms in the sealed carton; and e)cooling the pasteurized product within the carton so that by filling thecarton with product and then sealing the carton before the product isheated, no significant vacuum is created in the course of cooling theproduct.
 16. A method of shelf stable packaging a perishable liquid foodproduct in a gable top carton which is internally coated withthermoplastic and which includes sealing flaps which comprise side flapsand inwardly folded end flaps, the lower edge of each of said flapsbeing defined by a horizontal fold line where the flaps splay to formthe top of the carton, each of the flaps having an upper edge, the upperedge of the side flaps extending beyond the upper edges of the endflaps, one set of which end flaps being outwardly foldable to form aspout, the method comprising the sequential steps of:a) ensuring thatsaid liquid food product is free from pathogenic and thermophilicorganisms; b) filling the carton with the liquid food product maintainedat substantially room temperature; c) closing the carton so that thesealing flaps are adjacent one another; d) hermetically sealing thecarton containing said liquid food product at substantially roomtemperature by applying heat and a first level of pressure to firstportions of the sealing flaps that is sufficient to create hermeticseals at these portions of said sealing flaps, and applying lesserlevels of pressure to other portions of the sealing flaps.said lesserlevels of pressure being sufficient to provide a seal at these otherportions of the sealing flaps that in combination with the seal providedby the first level of pressure results in an overall seal which preventsbacteria from entering the carton through the sealing flaps, but whichlesser levels of pressure would not alone be sufficient to preventbacteria from entering the carton through the sealing flaps if appliedto both said first portions and said other portions of the sealingflaps, wherein the carton is easier to open than a carton in which allof the sealed portions of the sealing flaps have been sealed with thefirst level of pressure; e) heating the food product in the sealedcarton to a temperature sufficient for pasteurization but below thesoftening temperature of the thermoplastic coating; f) maintaining thefood product at the pasteurization temperature for sufficient time tokill essentially all microorganisms remaining within the sealed carton;and g) cooling the gable top carton and its pasteurized contents toprovide a shelf stable food product in a carton free from significantinternal vacuum.
 17. A method as in claim 16 wherein the liquid foodproduct contains no artificial preservatives.
 18. A method as in claim17, wherein the liquid food product remains shelf stable withoutrefrigeration for at least three months.
 19. A method as in claim 16wherein the temperature of the liquid food product at the time offilling into the carton is in the range of 60°-80° F.
 20. A method as inclaim 16 wherein the liquid food product is filled into the carton thatis open to the environment.
 21. A method of shelf stable packaging aperishable liquid food product in a four-sided carton having a gable topwhich is internally coated with thermoplastic and which includes sealingflaps comprising two opposed side panels terminating in upper side flapsand two opposed end panels terminating in inwardly foldable upper endflaps, a lower edge of each of said side flaps and end flaps beingdefined by a horizontal fold line where the side panels splay to formthe top of the carton, each end flap having a central vertical fold lineto permit inward folding of the end flap so that the inner faces of theend flaps contact adjacent inner faces of the side flaps when the gabletop is closed, and each of the flaps having an upper edge, the upperedges of the side flaps extending beyond the upper edges of the endflaps, one of the end flaps being outwardly foldable to form a spout,the method comprising the steps in sequence of:a) ensuring that theliquid food product is free from pathogenic and thermophilic organisms;b) filling the carton with the liquid food product maintained atsubstantially room temperature; c) closing the gable top containing saidliquid food product while the liquid food product is at ambienttemperature by inwardly folding each end flap so that the inner surfacesof the side flaps abut the adjacent inner surfaces of the end flaps; d)hermetically sealing the carton by applying heat and at least apredetermined first pressure to the side flaps that is sufficient toprovide a hermetic seal along a horizontal stake line above and closelyadjacent to the upper edges of the end flaps, along at least onevertical stake line extending from the lower edges of the side flaps tointersect the horizontal stake line near one end of the horizontal stakeline, and over a first central region covering a portion of the verticalfold lines of both end flaps extending downwards from the upper edge ofthe end flaps but not so far as to include the area at the intersectionof the vertical fold lines and the horizontal fold lines, and applyinglesser amounts of pressure to a second central region covering a portionof the vertical fold lines of both end flaps not covered by the firstcentral region and to any remaining portions of the side flaps whereinthe seals provided by the predetermined first pressure and the lesseramounts of pressure are together sufficient to prevent bacteria and airfrom entering the carton through the sealing flaps, but which saidlesser amounts of pressure applied across the end flaps would notthemselves provide seals sufficient to prevent bacteria and air fromentering the carton through the sealing flaps if applied across theentire sealing flaps, andwherein the carton so sealed by application ofthe predetermined first pressure and the lesser amounts of pressure iseasier to open than a carton in which all of the sealed portions havebeen sealed with the first predetermined amount of pressure; e) heatingthe food product in the sealed carton to a temperature sufficient forpasteurization but below the softening temperature of the thermoplasticcoating; f) maintaining the food product at the pasteurizationtemperature for sufficient time to kill essentially all microorganismsremaining within the carton; and g) cooling the gable top carton and itspasteurized contents.